View and Materialized View in SQL

View and Materialized View in SQL

View provides virtualized access to the database, while Materialized View stores pre-computed results for optimized query performance. We save the data as tables, but the concept of views comes in to customize the table’s accessibility. The table is kept in the database’s physical memory, and views are a concept of a virtual table that facilitates access to the actual table’s contents in a customized form. 

Get started with an understanding of how to create a SQL table. Views and Materialized Views in SQL have some significant differences that we will go over in this article. Before delving into the specifics of each realized view, let’s explore the fundamentals of views to better understand their differences.

Views in SQL

Views are produced by running a “SELECT query” statement, which creates a logical and virtual copy of a table. There is no storage for the views anywhere on the disc. Therefore, each time specific data is needed, a query must be run. However, the query expression is kept on the file system. There are no storage or update fees related to views. Because views are built with a certain architecture, defining a view requires adhering to an SQL standard. When data needs to be updated, access is often required, but only sometimes views are utilized.

Why should we use View?

Views are useful in SQL for some reasons. Whichever version of SQL you use (Oracle, SQL Server, MySQL, etc.), this holds ‘true’. Learn about RDBMS vs NoSQL

Simplifying SQL Queries

Using views primarily benefits you by making your queries simpler. Views are simply stored SQL statements, as we have already learned.

Example Scenarios:

• Choosing various columns
• Connections to further tables
• Functions, such as the aggregate functions
• WHERE sections
• COLLABORATION AND Possessing
• Thus, you can use a view to hold logic if you have a complex query or logic that is used frequently. When you require that data, you may then query from that view.

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Enhancing Security

Using views also has the benefit of enhanced security. A view that only chooses specific columns from a table can be made. Then, instead of the complete table, this view can be made available to specific users or apps. Explore what are primary and foreign keys in SQL

For example, if you have an employee table with wage details, not every program or user may want to access this wage data. Hence, you may make a view that excludes the salary columns from all of the data and then grant other users access to that view (but not the employee table).

This implies that they won’t see the wage information when they query the employee view.

Elements of Views

• A fundamental idea in databases is views, which have the following characteristics.
• Views are virtual tables that hold data according to the needs of the user.
• Many tables can be joined to construct views with ease, allowing us to generate the view we need from several tables.
• There are no additional storage fees related to views.
• Views make it possible to conceal the complexity of data, simplifying database management.

Syntax

CREATE [OR REPLACE] VIEW viewname AS

SELECT select_query;

It consists of multiple parts:

CREATE VIEW: Indicates that a view is being created.

OR REPLACE: You can replace an existing view with the same name using this optional query, so dropping it first is not necessary.

viewname: the desired view’s name. This will be referred to as this view in future requests.

AS SELECT: indicates that the view corresponds to the subsequent SELECT query.

select_query: the SELECT query that will be utilized for the view and kept on file. This query will run when you select from the view.

Example

CREATE VIEW emp_details AS

SELECT

emp_id,

last_name

FROM employee;

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View with Joins

Let’s see an example of joining two tables. One effective way to simplify the query is with this view. We’ll develop a view that presents all departmental and personnel data in a single view.

CREATE VIEW empdept AS

SELECT

e.emp_id,

e.last_name,

e.salary,

d.dept_id,

d.dept_name

FROM employee e

INNER JOIN department d ON e.dept_id = d.dept_id;

In doing so, a view that executes the join query is created. We may now query the view.

SELECT emp_id,

last_name,

salary,

dept_id,

dept_name

FROM empdept;

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View with Aggregate Functions

Let’s now see a view that makes use of aggregate functions. Assume for the moment that we were looking for each department’s name, ID, and total compensation, as well as its workforce size. This is how our SELECT query would appear:

SELECT

d.dept_id,

d.dept_name,

COUNT(e.*) AS emp_count,

SUM(e.salary) AS total_salary

FROM department d

INNER JOIN employee e ON d.dept_id = e.dept_id

GROUP BY d.dept_id, d.dept_name;

This illustrates the desired outcome. Let’s make this a view now.

CREATE VIEW dept_stats AS

SELECT

d.dept_id,

d.dept_name,

COUNT(e.*) AS emp_count,

SUM(e.salary) AS total_salary

FROM department d

INNER JOIN employee e ON d.dept_id = e.dept_id

GROUP BY d.dept_id, d.dept_name;

The query in the view is executed each time the view itself is queried, ensuring that the numbers are constantly current. This is possible because the view is a stored SQL statement rather than a distinct table. All we have to do now is query the dept_stats view to locate this data.

SELECT dept_id,

dept_name,

emp_count,

total_salary

FROM dept_stats;

If we only wanted to display data for a specific department, we could also use the WHERE clause to filter the view. Explore what joins are in SQL.

SELECT dept_id,

dept_name,

emp_count,

total_salary

FROM dept_stats

WHERE dept_id = 2;

Materialized View in SQL

Views with computed and stored contents are called materialized views. Similar to logical virtual tables, materialized views save the query’s result in the table or on the disc. Compared to regular views, the materialized views perform better. The reason for this is that the data is kept on the disc. 

Materialized views are sometimes referred to as “indexed views” since they provide faster and more efficient access to the table formed once the query is indexed. Learn about the types of indexes in SQL. When data must be retrieved often and table data is not updated frequently, materialized views are utilized. One of the three methods used by the database system to update the materialized view is

• As soon as the relation on which it is defined is modified, update the materialized view.
• Each time the view is accessed, update the materialized view.
• Periodically update the materialized view.

Advantages of Materialized View

Using materialized views in your database has various advantages.

Improved Query Efficiency

Using a materialized view primarily helps to increase a query’s efficiency. A lengthy query execution time may indicate the presence of numerous data transformations, such as joins, functions, and subqueries.

All of it may be combined into a single result set that is stored similarly to a table using a materialized view. This implies that instead of executing the costly query that makes use of joins, functions, or subqueries, any user or program that wants this data can just query the materialized view directly, as though all of the data is in one table. What is oracle?

Simplifying a Query

A materialized view can be used to streamline a query, much like a standard view. Using a materialized view can assist in moving some of the logic from a query that uses a lot of joins and functions into the materialized view.

Disadvantages of Materialized View

Data Updates Must Be Configured: The database tables hold the information that is utilized to fill the materialized view. The information in these tables can be added, changed, or removed. The materialized view’s data must be updated when that occurs. Although it should be done automatically, it can be done manually as well.

Data Could Be Varying: The data in the materialized view might not match the data in the underlying tables since the data is stored independently in the materialized view. If you depend on or are anticipating consistency in the data, this could be a problem.

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Syntax in Materialized View

CREATE (Or REPLACE)  MATERIALIZED VIEW basicDetails 

AS

SELECT Rollno, Name

FROM Students

WHERE Class = “7”; 

Elements of Materialized View

• In contrast to normal views, materialized perspectives have the following characteristics, which make them equally significant.
• The query’s speed is maximized because the same subquery yields the materialized view.
• Users must actively update the data in materialized views, as they are not automatically updated. This will lessen the possibility of any errors occurring when updating.
• The materialized view generates a table that is indexed in the database for faster and more effective access. “Indexed views” is its other name.
• A background service called Snowflake aids in the automatic maintenance of materialized perspectives.

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Syntax – Materialized View

CREATE MATERIALIZED VIEW viewname

[REFRESH [FAST|COMPLETE|FORCE] [ON DEMAND|ON COMMIT]]

[BUILD IMMEDIATE|BUILD DEFERRED]

AS

select_query;

It contains,

CREATE MATERIALIZED VIEW: Describe the materialized view that is being formed.
viewname: the new view’s name that has materialized.

REFRESH FAST: employs a log file’s modifications to the underlying tables as part of an incremental refresh technique.

REFRESH COMPLETE: repeats the query in the materialized view to perform a full refresh.

REFRESH FORCE: specifies that a full refresh is carried out if a quick refresh is not feasible. Among Complete, Force, and Fast, Force is the default.

REFRESH ON DEMAND: indicates that whenever certain package functions are invoked, a manual refresh will take place. By default, On Demand is used.

REFRESH ON COMMIT: denotes that if a transaction commits that modifies any of the underlying tables, a quick refresh takes place.

BUILD IMMEDIATE: Data will be added to the materialized view instantly. This is how things are by default.

BUILD DEFERRED: After the subsequent refresh, the materialized view is filled in.

AS select_query: The executed query, the output of which is kept in the materialized view.

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Example

CREATE MATERIALIZED VIEW empdept AS

SELECT

e.emp_id,

e.last_name,

e.salary,

d.dept_id,

d.dept_name

FROM employee e

INNER JOIN department d ON e.dept_id = d.dept_id;

We can now query the materialized view ‘empdept’:

SELECT emp_id,

last_name,

salary,

dept_id,

dept_name

FROM empdept;

Difference between View and Materialized View

Similar to a table, a database object holds data so it can be queried. That is, however, different.

The way it is refreshed is the primary difference between a view and a materialized view.

You would need to locate and use the initial script to change the data in the table or execute a MERGE statement if you wanted to refresh a table with information from other tables. To refresh a materialized view, simply run a command. Because it contains the query used to fill the data saved with it, the materialized view is aware of what has to be done. 

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Views are nothing more than a cached query that is executed whenever the view is requested. The parameters of the materialized view determine how often the data is updated, which is stored on a disc. This table explains a few of the variations.

Conclusion

Views are useful database objects that can make your queries easier to understand and increase system security. By keeping data in an accessible object, materialized views also greatly simplify queries and enhance query efficiency. Be cautious when generating too many views, as they might complicate matters and cause problems for your database. However, when used appropriately, views can be useful. Join the SLA Institute for the best Oracle SQL training in Chennai and explore a wide range of opportunities in the database domain.

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